A wireless communication method has been known in which access control based on CSMA is performed to obtain a right to transmit by carrier sensing and, when a right to transmit is obtained, a data packet transmission is started.
For access control, methods in which the probability of collision between data packets transmitted by an own communication device/apparatus (i.e., a subject apparatus) and other communication devices/apparatuses is reduced as much as possible are known. Such methods of access control include, for example, access control based on p-persistent CSMA in which a data packet transmission is started when a collision avoidance time determined based on a probability p elapses after an uncongested state of the wireless channel to be used is detected by carrier sensing and access control based on CSMA/CA complying with the IEEE802.11 standard in which backoff control is started when a predetermined amount of time elapses after an uncongested state of the wireless channel to be used is detected by carrier sensing and in which carrier sensing is continued during a randomly determined collision avoidance time.
A communication device which performs such access control based on CSMA sets an access control start time or data packet collision avoidance time autonomously without regard to other communication devices, so that, when there are more communication devices to use a same wireless channel, there is a higher probability of the access control start time or data packet collision avoidance time coinciding with different communication devices.
When CSMA access control is used, therefore, it is not possible to prevent, certainly, transmission packets transmitted by plural communication devices from colliding with one another, so that there have been cases where the number of data packet transmissions cannot be evenly distributed among communication devices.
To solve such a problem, a method of evenly distributing the number of transmissions among the communication devices has been proposed (see Japanese patent document JP-A-2005-311885, for example) in which the time from when each communication device successfully completes a data packet transmission to when the communication device next obtains a right to transmit by access control is measured as the transmission waiting time of the communication device and the number of data packets the communication device is allowed to transmit based on the obtained right to transmit is determined based on the measured transmission waiting time.
In the proposed wireless communication method, when a communication device is unable to transmit a data packet on an occasion, the number of data packets the communication device is allowed to transmit on the next occasion is increased, so that the volumes of data transmitted by plural communication devices are eventually averaged. Thus, the method is not for preventing collisions between data packets transmitted by plural communication devices. It is not, therefore, possible, using the method, to average the data packet transmission intervals among plural communication devices and allow each of the communication devices to carry out a transmission at a constant period.
Thus, the proposed method can be applied to a system in which each communication device is required to transmit a large volume of data divided into many packets, but it cannot be applied to a system in which each communication device is required to periodically transmit varying control data without involving any delay in responses.